The present invention generally relates to facilities and apparatuses suitable for operation in extraterrestrial environments, and more particularly to processes and facilities for extracting oxygen from minerals that can be found on planets, planetoids, etc.
Oxygen extraction from in situ space minerals is valuable for life support, propulsion, and as a chemical reagent for use in outer space travel. It may be argued that an efficient means for oxygen production has the potential to dramatically accelerate space travel, space-based economic development, and settlement on worlds beyond earth. An in situ resource utilization (ISRU) facility capable of producing many times its own launch weight in oxygen would dramatically lower mission mass and cost for subsequent travel to oxygen depots and beyond. As such, an organization operating such a depot in space (for example, on a planet, planetoid, or manmade satellite or space station) could charge a premium for this valuable commodity.
Oxygen extraction methods favored by, for example, the United States National Aeronautics and Space Administration (NASA), include molten oxide electrolysis (MOE), hydrogen reduction of ilmenite (FeTiO3), and carbo-thermal reduction of ilmenite. These methods were apparently down-selected from a number of candidate methods. Although the above three methods represent a relative degree of maturity, the technical limitations of each make it unclear that they can achieve the efficiency, convenience, and weight leverage performance metrics needed for a profitable ISRU oxygen depot.
MOE involves electrolysis of molten minerals by inserting a cathode and an anode into a heated vat of liquid rock, applying a potential to the electrodes to cause oxygen bubbles to form and rise from one of the electrodes, and then capturing the oxygen. Although MOE is simple in concept, tremendous demands are placed on the electrode material, such that a long-lived component may be difficult or impossible to construct, necessitating a substantial number of spare parts. Heating of the molten minerals is also a challenge, and limits the scale of the device. The crude nature of this simple concept also does not lend itself to a clean and easily-maintained apparatus.
Hydrogen and carbo-thermal reduction of ilmenite are akin to chemical reactor processes on earth. Either hydrogen or methane is heated to an elevated temperature to shift the oxygen atoms from crushed and beneficiated minerals onto another molecule. The oxygen atoms are isolated in a second step, such as electrolysis of water, and the resulting hydrogen or hydrocarbon gas is available as a useful byproduct or for recycling. Key challenges for ilmenite reduction include the need to avoid all leaks of process gasses. For lunar processing, any loss of reaction gasses must be made up with a resupply of those gasses from earth. A simple system would require a larger mass of resupply; a more complex system (such as double-wall containment) would demand a larger factory launch mass. Furthermore, the use of ilmenite requires that this specific mineral be selectively removed from regolith, or powdered rock, that blankets the Moon and other airless planetoids. Ilmenite beneficiation has been demonstrated with analog materials, but the ability to do so in the harsh environment of the lunar surface cannot be proven without experiments in the actual operating environment. Also, ilmenite is not uniformly distributed across the Moon, so that certain locations are less suitable than others. These factors detract from the appeal of ilmenite reduction.
Another limitation of the methods discussed above is the need for gravity to accomplish the process steps, necessitating the placement of the ISRU facility on a planet.
In view of the above, an ISRU facility for oxygen extraction would likely be more technologically and commercially successful if capable of a high ratio of oxygen produced-to-factory launch mass, simple or autonomous operation, low mass of spare parts, the ability to operate in low-gravity (e.g., a planetoid) and microgravity (e.g., orbital) environments, and insensitivity to regolith feedstock.